Activity Regulation Of Ultra-small Cobalt Ferrite Nanozymes And Their Catalytic Applications

Nanozymes are inorganic nanomaterials with enzyme-like catalytic activity,which have the advantages of high stability,easy large-scale synthesis and low cost.Ferrite nanomaterials are a typical class of peroxide-like nanoenzymes,which were first discovered to have peroxidase-like activity in 2007 and have become an important platform material for nanoenzyme applications.In recent years,ferrite nanomaterials have shown attractive prospects for biomedical applications such as tumour catalysis,in vitro diagnostics,antioxidant therapy and antibacterial applications.It has been shown that the peroxidase-like activity of different ferrite nanomaterials is closely related to the size and fraction of the material,however,the size and fraction-dependent regulation of peroxidase-like activity is still unclear.In response to this problem,in this paper,we use ferrite nanoparticles as platform materials to prepare ferrite nanoparticles of different sizes and compositions,we have systematically studied the size-and component-dependent peroxidase-like activities,which provide experimental and theoretical basis for the construction of highly efficient catalytic ferrite nanozymes.Based on the catalytic mechanism of ferrite-like peroxidase-like Fenton reaction,by regulating material factors（size,composition,surface modification）and environmental factors（substrate concentration,interfering ions,culture medium environment,temperature and p H,etc.）,elucidated its size-and component-dependent peroxidase-like activity,optimized the structure of ferrite nanozymes and improved its peroxidase-like catalytic activity.Through the optimized ultra-small cobalt ferrite nanozyme,we have carried out application research in the degradation of tetracycline and methylene blue and other pollutants.In addition,we also constructed transferrin-coupled ultra-small cobalt ferrite nanozymes for tumor immunohistochemical staining applications to detect tumor tissues with high sensitivity,laying a foundation for the development of nanozyme-based in vitro diagnostic technology to provide a better platform material.The main research contents of this paper are as follows:（1）We first synthesized cobalt ferrite nanoparticles with a series of sizes to study the effect of size on the POD activity of ferrite nanoparticles.The TEM results showed that the prepared Co Fe₂O₄nanoparticles were regular in shape and spherical,and their average particle sizes were 3.1±0.25 nm,6.03±0.5 nm,13.5±0.9 nm and 17.7±1.4 nm.Through the POD enzyme catalytic activity test,it is clear that the enzyme-like catalytic activity of Co Fe₂O₄nanoparticles has an exponential dependence on the particle size,that is,the smaller the size,the more metal ions exposed on the surface,and the stronger the enzyme-like catalytic activity.Different transition metal ion-doped ultra-small（Sub-5 nm）ferrite nanoparticles were successfully prepared by dynamic simultaneous thermal decomposition method,Co Fe₂O₄,Mn Fe₂O₄,γ-Fe₂O₃respectively.The structure of the nanoparticles was characterized by TEM,XRD,XPS,VSM,DLS,Zeta potential and FT-IR and other test methods.According to the test results of TEM,XRD and XPS,the analysis shows that the morphology of the nanoparticles is uniform,the size distribution is narrow,and the nanocrystals are typical spinel structures.VSM test results show that the saturation magnetization of ultra-small Mn Fe₂O₄,γ-Fe₂O₃,and Co Fe₂O₄nanoparticles are27.5 emu/g,25.6 emu/g,and 22.4 emu/g,respectively.DLS,Zeta potential and IR results showed that the oil phase nanoparticles were successfully transferred to the water phase by ligand exchange reaction,and the hydrated particle size results showed that the nanoparticles had good dispersion stability within 15 days.（2）We regulated the POD-like activity of ferrite nanoparticles by material factors and environmental factors.Firstly,the surface ligand molecules were optimized to modify ultra-small ferrite nanozymes,and the nanoparticles modified by DHCA ligand molecules with the highest enzyme-like catalytic performance.Subsequently,we further studied the role of components in the catalytic activity of ultra-small ferrite nanoparticles.The results of enzyme activity tests showed that the catalytic activities of nanoparticles were dependent on components at different p H,expressed as Co>Mn>Fe.So far,we have constructed high-performance ultra-small cobalt ferrite nanozymes for subsequent experiments.By evaluating the catalytic stability of ultra-small cobalt ferrite nanoparticles POD-like enzymes in the environment of interfering ions/cell culture medium,the experimental results prove that the nanoparticles are expected to generate a large amount of ROS in living cells for integrated platform materials for disease diagnosis and treatment.（3）The ultra-small cobalt ferrite nanozyme with the strongest catalytic activity was applied to the degradation of pollutants,and the degradation performance of this nanozyme was evaluated.The experimental results show that the ultra-small cobalt ferrite nanozyme exhibits good catalytic degradation performance for common pollutants in water such as tetracycline and methylene blue,and the degradation efficiency of the two pollutants reaches more than 95%within 20 mins.（4）Utilizing the strong peroxidase-like catalytic activity of ultra-small cobalt ferrite nanozymes,the surface of the particles is coupled to the surface of tumor cells to overexpress transferrin Tf R1-specific antibody Tf,and the nanozyme system is used for immunohistochemical qualitative detection tumor tissue.The experimental results show that the ultra-small cobalt ferrite nanozyme can improve the detection sensitivity in the tissue section staining of mouse breast cancer tumor model compared with traditional Prussian blue staining,which provides a new choice for immunohistochemical staining technology based on nanozyme.